1. Field of the Invention
The present invention relates to an electronic apparatus having a battery power source, for example, a portable information terminal such as a PDA (Personal Digital Assistant), a PC (Personal Computer), or a PHS (Personal Handyphone System), or a portable game machine to which a function can be added by a peripheral device such as a memory card, or a modem which is driven by a primary or secondary battery.
The present invention relates also to an electronic apparatus, and particularly to a configuration wherein a power is supplied from a battery to a card-like electronic part such as a PCMCIA (Personal Computer Memory Card International Association) card which is attached to the electronic apparatus and on which an electronic circuit is mounted.
2. Description of the Related Art
FIG. 21 is a diagram showing the configuration of a prior art electronic apparatus which comprises a usual power source circuit having a voltage monitoring circuit for a battery. Referring FIG. 21, the voltage of the battery 1 is boosted by a boost circuit 2 and a stable driving voltage is supplied to the system main unit 3 of the electronic apparatus. A voltage monitoring circuit 4 detects a voltage which appears immediately before the capacity of the battery 1 is reduced to reach the operating limit of the system main unit 3 of the electronic apparatus, and warns the system 3.
FIG. 22 shows the flow of a process of checking the battery which is conducted when the electronic apparatus of FIG. 21 is activated. The power source circuit is turned on at step S1, and the system main unit 3 is initialized at step S2. The voltage monitoring circuit 4 detects at step S3 the voltage of the battery 1, and compares at step S4 with the detected voltage with a preset reference voltage.
If the detected voltage is higher than the reference voltage, the process proceeds to step S6 in which the process waits for a start of a computer program application. If the detected voltage is equal to or lower than the reference voltage, the process proceeds to step S5. At step S5, it is judged that the voltage reaches the warning level and a process of driving a warning sign 14 which warns the user is conducted.
The processes of steps S1 to S3 are conducted by the voltage monitoring circuit 4 shown in FIG. 21, so that the voltage just above that which is the operating limit at activation of the system main unit 3 of the electronic apparatus is detected and a detection signal a is output. In response to the detection signal a, the system main unit 3 causes an interruption in the program and performs the process of driving the battery warning sign 14 such as a display of a battery warning mark, a display of a message requesting replacement of the battery, or emission of an alarm sound.
FIG. 23 shows the flow of a process of improving the state of the power source in the prior art apparatus of FIG. 21. When the voltage monitoring circuit 4 of FIG. 21 detects that the voltage of the battery is equal to or lower than the reference voltage of a value just above the operating limit of the system main unit 3, the battery warning sign 14 is displayed at step S7 and it is checked at step S8 whether the battery is to be replaced or not.
When the battery is to be replaced, the power is turned off. When the battery is not to be replaced, the process proceeds to step S9 in which it is judged whether the power supply is switched to an external power source or not. When the power supply is switched to an external power source, the display of the battery warning sign is turned off. In other words, the battery warning sign 14 is continued to be displayed until replacement of the battery or start of the power supply from an external power source such as an AC adaptor is conducted at steps S8 and S9.
FIG. 24 shows the flow of a process in the case where the state of the power source is returned in the prior art apparatus of FIG. 21. Referring to FIG. 24, if it is judged at step S10 that the battery is to be replaced, the power is once turned off and the battery is replaced with a fresh one. Thereafter, the power is again turned on. Because of the power-off due to the battery replacement, therefore, no power is supplied to the system main unit 3 and the so-called manual cancellation is performed. Consequently, after the battery replacement is done, the system main unit 3 is again initialized. When the power supply is switched to an AC adaptor which is an external power source, an input from an external power source terminal 15 is detected at step S11. When the recovery of the voltage due to the external power source is detected, the display of the battery warning sign 14 is turned off.
As described above, in the power source circuit of the prior art, the voltage monitoring circuit 4 measures merely the terminal voltage of a battery, and, when the terminal voltage is equal to or lower than the preset reference voltage, the battery replacement warning is given. According to such a configuration, information of the state of the battery cannot be obtained unless the voltage of the battery is lowered to the preset warning level of the system main unit 3. In other words, there is a problem in that, even when the terminal voltage of a battery reaches a reference level, it is impossible to obtain information regarding the magnitude of the load which can be driven by the remaining capacity of the battery.
The prior art apparatus has another problem as follows. In the case where the voltage of a battery is lowered to a level which is equal to or lower than the preset warning level, when an operation involving a large load, such as access of a peripheral device 16 is conducted, the voltage of the battery is further lowered, resulting in that the system main unit 3 falls into a disfunctional state and data which are currently produced in the system main unit 3 disappear.
The prior art apparatus has a further problem in that, when the state of the power source is improved as a result of replacement of a battery, connection to the AC adaptor, or the like, a special operation must be performed on the electronic apparatus and the user is required to perform a special operation such as initialization of the system main unit 3 or restart of the apparatus.
FIG. 25 is a circuit diagram illustrating a prior art electronic apparatus to which a PCMCIA card can be attached. In the figure, 200 designates an electronic apparatus having a slot 200a to which a PCMCIA card 201 is to be attached. The electronic apparatus 200 has an external power source terminal 200b to which an external power source is to be connected through an AC adaptor or the like, and is configured so as to incorporate a battery. The power supply to the PCMCIA card 201 is performed also by a battery 202.
The electronic apparatus 200 comprises a CPU (Central Processing Unit) 200a which performs required calculation processes, a ROM (Read-Only Memory) 200b which stores programs for the calculation processes and the like, and another functional circuit 200c. These components are configured in the form of an LSI chip. The apparatus 200 further comprises a boost circuit 220 which generates a voltage (5 V) required for operating the LSI chips such as the CPU 200a and the ROM 200b.
A diode (D3) 225 is forward connected between the external power source terminal 200b and the boost circuit 220, and another diode (D2) 224 is forward connected between the battery 202 and the boost circuit 220.
The boost circuit 220 comprises a coil (L1) 222 one end of which is connected to the cathodes of the diodes 224 and 225, a diode (D1) 223 the anode of which is connected to the other end of the coil 222, and a power source IC 221 which is connected between the ends of the diode 223 and the ground.
The output of the boost circuit 220 is connected to the slot 200a through a switching element 211 composed of a field effect transistor FET1. When the electronic apparatus 200 is powered on, the gate input PC of the switching element 211 reaches the on-level of the transistor FET1 and the power is supplied to the PCMCIA card 201 through the switching element 211.
However, the prior art electronic apparatus to which a PCMCIA card can be attached and which is configured as described above has the following problems.
In the prior art electronic apparatus 200, although a wide variety of PCMCIA cards which are largely different in level of the operation current are used., the power supply is conducted on any kind of PCMCIA card in the same manner. In the case where the remaining capacity of the battery of the electronic apparatus is insufficient or where a PCMCIA card requiring a driving current exceeding the load driving capacity of the battery is to be driven, when a PCMCIA card is connected to the battery, therefore, a current of a level required for driving the card momentarily flows through the card. Such a momentary current may adversely affect the electronic apparatus, with the result that the electronic apparatus is caused to run away or the LSIs and the like incorporated in the electronic apparatus are broken in some cases.
When a modem card requiring a large operating current is attached to the electronic apparatus incorporating a battery which is in the last stage of the life (where there is only small capacity, for example), the power source voltage (5 V) which is necessary for the CPU, the ROM, etc. mounted on the electronic apparatus, and also the PCMCIA card to operate, cannot be secured. This may cause the electronic apparatus to malfunction.
In many electronic apparatuses, as described above, in addition to a power supply using a battery, also an external power supply using an AC adaptor can be utilized. Even when the remaining capacity of the battery is insufficient for the electronic apparatus to operate, such an electronic apparatus is enabled to operate normally by the external power supply.
Assume a case where such an electronic apparatus is operated by the external power supply and the remaining capacity of the battery is insufficient for the electronic apparatus to operate. In such a case, when the external power supply is stopped by a power failure or the like, there arises a problem in that the apparatus malfunctions because of the insufficient remaining capacity of the battery.
Japanese Unexamined Patent Publication JP-A 1-94493 (1989) discloses an ID card which may be used as an article management card in a production line and which comprises a built-in battery, a data processing circuit driven by the battery, and a transmission circuit for conducting communication between the data processing circuit and an external apparatus. In the ID card, when the output voltage of the battery is lowered to a predetermined voltage reduction detection level, the external apparatus is informed of the reduction of the output level of the battery. This prevents a stop of the operation of the ID card due to the phenomenon that the output level of the battery is lowered to the malfunction level of the ID card, from occurring during a period when the production line is operating.
However, the technique disclosed in the publication is to detect the reduction of the output level of the battery in the ID card and prevent the ID card from malfunctioning, and is not directed to an electronic apparatus to which various PCMCIA cards of different driving currents can be attached and which drives the attached card. Therefore, the disclosed technique cannot solve the problems caused in such an electronic apparatus by an inrush current which, when a power source is connected to a PCMCIA card, is produced because of the reduction of the voltage driving the PCMCIA card or a difference in level among driving currents of cards.
The present invention solves the foregoing problems. It is an object of the invention to provide an electronic apparatus in which an inrush current (produced when a card-like electronic part such as a PCMCIA card is attached to the body of the electronic apparatus and connected to a battery disposed in the body) can be suppressed, whereby runaway of the apparatus and breakage of the internal circuit due to the inrush current are prevented from occurring.
It is another object of the invention to provide an electronic apparatus in which, even when an external power supply is stopped by a power failure or the like under a state where the apparatus is operated by the external power supply, malfunction of the apparatus due to an insufficient remaining capacity of a battery can be prevented from occurring.